If you're getting an "Extensions unavailable" error as pictured above, you've probably got duplicate VCaaS processes running. To check and possibly fix this, go into Task Manager (Ctrl-Alt-Delete) and select the Details tab as shown below.
If you have multiple instances of Communicator.exe or VCaaS_Communicator running then that is likely your problem. But either way, right-click on any such instances and choose the End task option. Restart VCaaS and (hopefully) your problem is fixed.
This is most often (always?) caused by having two different versions of VCaaS installed simultaneously. If so then remove the old version or at least disable the old version from starting automatically.